It is known to provide, upstream along a cold-water line of an electrical power plant condenser, a screening device or apparatus which is utilized for the mechanical removal of solids from the water stream. The device can comprise a cylindrical housing which is formed with a screen surface through which the cooling water passes so that solids can collect upon this surface. A rotating suction device is juxtaposed with the screen surface and can draw the contaminants therethrough for a partial backwashing of the screen surface.
The rotating suction device is thus connected to a mechanical drive for effecting the continuous or intermittent rotation. The mechanical cleaning of a water stream with such a device has been associated with a thermodynamic problem which can be manifested as an entropy reduction. For cleaning of the screen in this manner, cleaning work must be done and invariably results in a pressure loss. The device just described has been characterized as a differential pressure screen apparatus and because of pressure losses associated with the cleaning operation, efficiency is comparatively poor.
One such device is described in Bulletin IK 1982 of the Atlantik Geratebau GmbH of the German Federal Republic and utilizes a vessel to form the housing and designed in accordance with pressurized container techniques. The static pressure of the cooling water must, however, be high for this system to be useful. In this system, the cooling water inflow is effected radially via a fitting on the container shell and the outflow of the cooling water beyond the screen is likewise radial via a fitting connected to the housing shell.
The cooling water flow to the container thus has an S-pattern. The fittings required are associated with static problems with respect to strength and stability, create assembly problems and result in a high capital cost for the unit.
The screening element of the container is generally mounted between two portions of the container shell in the form of screening cylinders or cartridges, (e.g. so-called filter candles).
The rotating suction device is provided with an axially extending suction duct which simultaneously forms the shaft on which the rotating unit can be orbited and the shaft extends axially out of an axial end of the housing where it is coupled to the transmission or speed reducing gearing of an electric motor. Service openings are provided in the container cover or covers and are closed by corresponding plates.
The arrangement whereby the shaft and the suction duct extend axially through the container and the inlet and outlet for the main water stream communicate radially therewith has been found to give rise to such considerable pressure losses as to make the utility of the apparatus questionable in many cases.